System and method for suppressing the formation of oxygen inclusions and surface blisters in glass sheets and the resulting glass sheets

ABSTRACT

A system and method for suppressing the formation of gaseous inclusions in glass sheets and the resulting glass sheets are described herein. The system includes a melting, fining, delivery, mixing or forming vessel that has a refractory metal component (e.g., platinum component) which has an inner wall that contacts molten glass and an outer wall coated with an oxygen ion transportable material (e.g., zirconia) which is coated with a conductive electrode. The system also includes a DC power source that supplies DC power across the oxygen ion transportable material which causes oxygen ions to migrate from the refractory metal component to the conductive electrode and enables one to control the partial pressure of oxygen around an exterior of the vessel which helps one to effectively prevent hydrogen permeation from the molten glass in order to suppress the formation of undesirable gaseous inclusions and surface blisters within the glass sheet. The present invention also helps one to effectively reduce the oxidation of external, non-glass contact surfaces of the refractory metal component.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for suppressing theformation of oxygen inclusions and surface blisters in glass sheets andthe resulting glass sheets.

2. Description of Related Art

Liquid crystal displays (LCDs) are flat panel display devices thatinclude flat glass substrates or sheets. The fusion process is apreferred technique for producing sheets of glass used in LCDs becausethe fusion process produces sheets whose surfaces have superior flatnessand smoothness compared to sheets produced by other methods. The fusionprocess is described in U.S. Pat. Nos. 3,338,696 and 3,682,609, thecontents of which are incorporated herein by reference.

Many of the glass sheets manufactured for flat panel displayapplications, particularly those formed by the fusion process (alsoreferred to as the downdraw process or the slot draw process), aremelted and formed with components made from refractory metals, e.g.platinum or platinum alloys. This is particularly true in the fining andconditioning sections of the fusion process, where refractory metals areemployed to minimize the creation of gaseous inclusions within the glasssheets. To further minimize the creation of gaseous inclusions withinthe glass sheets, the fusion process often employs arsenic as a finingagent. Arsenic is among the highest temperature fining agents known,and, when added to the molten glass bath, it allows for O₂ release fromthe glass melt at high melting temperatures (e.g., above 1450° C.). Thishigh temperature O₂ release, which aids in the removal of bubbles duringthe melting and fining stages of glass production, coupled with a strongtendency for O₂ absorption at lower conditioning temperatures (whichaids in the collapse of any residual gaseous inclusions in the glass),results in a glass sheet that is essentially free of gaseous inclusions.From an environmental point of view, it would be desirable to providealternative methods of making such high melting point and strain pointglass sheets without having to employ arsenic as a fining agent.

It would also be desirable to find alternative methods for making suchglass sheets via the downdraw process in which the glass sheets havevery little if any gaseous inclusions or surface blistering. One suchmethod is described in U.S. Pat. No. 5,785,726 which discloses ahumidity controlled enclosure that surrounds all or a portion of aplatinum-containing vessel and is used to control the dew point outsidethe vessel in order to reduce the formation of gaseous inclusions inglass sheets. Another method for reducing the formation of gaseousinclusions in glass sheets is described in U.S. Pat. Nos. 6,128,924 and5,824,127 which disclose the use of various batch constituents tominimize the water content in the glass composition and thus thehydrogen concentration on the inside surface of the platinum-containingvessel. Although the methods disclosed in the patents mentioned abovesuccessfully reduce the formation of gaseous inclusions in glass sheetsformed in systems utilizing platinum-containing vessels, it would bedesirable to provide alternative methods to prevent the formation ofgaseous inclusions in glass sheets.

BRIEF DESCRIPTION OF THE INVENTION

The present invention includes an alternative system and method forsuppressing the formation of gaseous inclusions in a glass sheets andthe resulting glass sheets. The system includes a melting, fining,delivery, mixing or forming vessel that has a refractory metal component(e.g., platinum component) which has an inner wall that contacts moltenglass and an outer wall coated with an oxygen ion transportable material(e.g., partially or fully stabilized zirconia) which is coated with aconductive electrode. The system also includes a DC power source thatsupplies DC power across the oxygen ion transportable material whichcauses oxygen ions to migrate from the refractory metal component to theconductive electrode and enables one to control the partial pressure ofoxygen around an exterior of the vessel which helps one to effectivelyprevent hydrogen permeation from the molten glass in order to suppressthe formation of undesirable gaseous inclusions and surface blisterswithin the glass sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be had byreference to the following detailed description when taken inconjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram illustrating an exemplary system in accordancewith a first embodiment of the present invention;

FIG. 2 is a partial cross sectional side view of one of the vessels usedwithin the system shown in FIG. 1;

FIG. 3 is a flowchart illustrating the basic steps in a method forsuppressing the formation of oxygen inclusions and surface blisters inglass sheets in accordance with the present invention;

FIG. 4 is a block diagram illustrating an exemplary system in accordancewith a second embodiment of the present invention;

FIG. 5A (prior art) is a schematic that illustrates the hydrogenpermeation reaction that occurs without the oxygen extraction technologyof the present invention;

FIG. 5B is a schematic that illustrates the hydrogen permeation reactionthat occurs with the oxygen extraction technology of the presentinvention;

FIG. 6 is a graph that illustrates the impact of the oxygen level on thepartial pressure of hydrogen around the external surface of the systemsshown in FIGS. 1 and 4;

FIG. 7 is a diagram of an experimental set-up used to verify the oxygenextraction technology of the present invention;

FIG. 8 is a graph that illustrates data which shows a decrease inpartial pressure of oxygen at an interface of a Pt tube and glass whencurrent is applied across a zirconia layer in the experimental set-upshown in FIG. 7; and

FIG. 9 is a graph that illustrates data which shows the impact of thedewpoint on the partial pressure of oxygen at the interface of the Pttube and glass in the experimental set-up shown in FIG. 7.

DETAILED DESCRIPTION OF THE DRAWINGS

Before describing exemplary embodiments of the present invention, itshould be understood that the present invention is not limited to thedetails of construction or process steps set forth in the followingdescription. In fact, the present invention is capable of otherembodiments and of being practiced or carried out in various ways.

The present invention is directed to a method of forming glass sheets ina manufacturing system which employs at least one vessel that contains arefractory metal component (e.g., platinum-containing component). Thepreferred glass sheets are aluminosilicate glass sheets or borosilicateglass sheets. And, the preferred process for manufacturing these glasssheets is the downdraw sheet manufacturing process. As used herein, thedowndraw sheet manufacturing process refers to any form of glass sheetmanufacturing process in which glass sheets are formed while travelingin a downward direction. In the fusion or overflow downdraw formingprocess, molten glass flows into a trough, then overflows and runs downboth sides of a pipe, fusing together at what is known as the root(where the pipe ends and the two overflow walls of glass rejoin), and isdrawn downward until cool. The overflow downdraw sheet manufacturingprocess is described in U.S. Pat. No. 3,338,696 (Dockerty) and U.S. Pat.No. 3,682,609 (Dockerty) both of which are hereby incorporated byreference herein. This technique is capable of forming very flat andthin glass sheets.

Other forms of downdraw sheet forming techniques include the slot drawand redraw forming techniques. In the slot draw technique, molten glassflows into a trough having a machined slot in the bottom. The sheets ofglass are pulled down through the slot. The quality of the glass sheetsis dependent on the accuracy of the machined slot. The redraw formingtechnique generally involves preforming a glass composition into a blockof some shape, then reheating and drawing the glass downwardly into athinner sheet product.

All of these manufacturing techniques in which silicate glass is meltedand formed into glass sheets utilize one or more vessels that have aglass contacting material which contains a refractory metal such asplatinum because of its inert properties. Unfortunately, platinumenables hydrogen migration to occur from the glass melt through theplatinum, thereby creating an oxygen rich layer at the glass/platinuminterface which can lead to the formation of undesirable gaseous oxygeninclusions or surface blisters in the glass.

While not wishing to be bound by theory, it is believed that the surfaceblistering effect which occurs in platinum vessels, for example, occursas a result of the formation of an oxygen rich layer near theplatinum-glass melt interface. This oxygen rich layer in the glass isbelieved to be produced by a combination of thermoelectric electrolysisof the glass melt, breakdown of oxide fining agents, and the number ofOH groups dissolved in the glass. The latter effect is believed to havea large impact on the rate of blistering as a result of the contact ofthe glass with the platinum. It is also believed that OH groupsdissociate into neutral hydrogen and oxygen. The hydrogen then permeatesthe platinum skin, enriching the surface region (platinum contactingregion) of the glass with oxygen which can then form bubbles in theglass if the solubility limit of the glass is exceeded. In particular,the hydrogen permeation blistering occurs due to the loss of hydrogenfrom the glass when the partial pressure of hydrogen at theglass/platinum interface is higher than the partial pressure of hydrogenat the external surface of the platinum vessels (see FIG. 5A). Thepresent invention helps reduce the undesirable bubble generation bycontrolling reactions that occur at the boundary layer between theplatinum skin and glass. An exemplary glass delivery system 100 inaccordance with the present invention is described below with respect toFIGS. 1-6.

Referring to FIG. 1, there is shown a schematic view of the system 100for making glass sheets using the downdraw fusion process. The system100 includes a melting vessel 110 into which batch materials areintroduced as shown by arrow 112, and initial glass melting occurs inthe melting vessel 110. The melting vessel 110 is made from refractorymaterials. The system 100 further includes components that are typicallymade from platinum or platinum-containing metals. For example,platinum-containing metals include alloys of platinum, which may includePt—Rh, Pt—Ir, etc, and combinations thereof. The platinum-containingcomponents include a fining vessel 115 (e.g., finer tube 115), a mixingvessel 120 (e.g., stir chamber 120), a finer to stir chamber connectingtube 122, a delivery vessel 125 (e.g., bowl 125), a stir chamber to bowlconnecting tube 127, a downcomer 130, an inlet 132 and a forming vessel135 (e.g., fusion pipe 135). The fining vessel 115 is a high temperatureprocessing area for removing bubbles. The delivery vessel 125 deliversthe glass through the downcomer 130 to the inlet 132 and into theforming vessel 135 which forms a glass sheet.

Referring to FIGS. 2 and 3, there are shown a partial cross sectionalside view of one of the vessels 115 (for example) in the system 100 anda flowchart illustrating the steps in a method 300 for forming a glasssheet utilizing the system 100. According to a preferred embodiment ofthe invention, the platinum containing component 115, 120, 122, 125,127, 130 and 132 that is in contact with molten glass has an outer wall202 coated (step 302) with an oxygen ion transportable material 204(e.g., zirconia 204) which is then coated (step 304) with a conductiveelectrode 206. A DC power source 208 supplies (step 306) DC power acrossthe zirconia 204 which causes oxygen ions to migrate from the platinumcontaining component 115, 120, 122, 125, 127, 130 and 132 to theconductive electrode 206 and enables one to control the partial pressureof oxygen around an exterior of the platinum containing component 115,120, 122, 125, 127, 130 and 132 which helps to prevent hydrogenpermeation from the glass which causes oxygen rich blisters to form inthe glass. As shown, the DC power source 208 has a negative power lead210 connected to the platinum containing component 115, 120, 122, 125,127, 130 and 132 and a positive power lead 212 connected to theconductive electrode 206.

By applying the appropriate DC voltage with the appropriate polarityacross the zirconia 204, oxygen ions (O⁻²) migrate from the insidesurface of the zirconia 204 to the outside surface of the zirconia 204(see exploded view in FIG. 2). One molecule of oxygen gas is removedfrom the surface of the platinum containing component 115, 120, 122,125, 127, 130 and 132 for every two molecules of oxygen ions thatmigrate through the zirconia 204. This is due to the electron (e⁻) flowestablished by the DC power supply 208. As oxygen ions (O⁻²) leave theinterface between the external surface of the platinum containingcomponent 115, 120, 122, 125, 127, 130 and 132 and the zirconia 204, thepartial pressure of oxygen is reduced around the external surface of theplatinum containing components 115, 120, 122, 125, 127, 130 and 132. Therate of removal of the oxygen from the external surface of the platinumcontaining components 115, 120, 122, 125, 127, 130 and 132 isproportional to the current flow from the DC power source 208 as relatedby faraday's law. For example one can use the DC power source 208 tovary the voltage and current applied to the zirconia 204 in order tocontrol the magnitude of the partial pressure of oxygen so it is withinthe range of 1 to 10⁻¹⁰ atmospheres which enables one to tailor themagnitude of the partial pressure of hydrogen to any level required toprevent hydrogen permeation.

Two favorable reactions occur as the partial pressure of hydrogen israised and the partial pressure of oxygen is lowered on the externalsurface of the platinum containing component 115, 120, 122, 125, 127,130 and 132. First, the rate of hydrogen permeation from the glass isreduced due to a shift in the water, hydrogen and oxygen equilibrium atthe external surface of the platinum containing component 115, 120, 122,125, 127, 130 and 132. This reduction of hydrogen permeation from theglass helps suppress the formation of oxygen blisters in the glass (seeFIG. 5B). Secondly, the rate of oxidation of the platinum containingcomponent 115, 120, 122, 125, 127, 130 and 132 is reduced due to thelower availability of oxygen for the oxidation reaction.

Referring to FIG. 4, there is shown a schematic view of a system 100′ inaccordance with a second embodiment of the present invention. As shown,the system 100′ includes discrete sections of oxygen ion transportablematerial 204 a . . . 204 f (e.g., zirconia 204 a . . . 204 f), discreteconductive electrodes 206 a . . . 206 f and discrete DC power sources208 a . . . 206 f that enable one to control the hydrogen permeation atindividual sections of the system 100′. It should also be appreciatedthat the individual sections of the system 100′ may be connected to morethan one power supply 208. For example as shown, the fining vessel 115can have more than one power supply 208 a′ and 208 a″ (two shown).Alternatively, the system 100′ can be covered with the oxygen iontransportable material 204 (e.g., zirconia 204) and then covered withdiscrete conductive electrodes 206 a . . . 206 f and discrete DC powersources 208 a . . . 208 f that enable one to control the hydrogenpermeation at individual sections of the system 100′ (not shown).

The impact of the present invention on hydrogen permeation can bedemonstrated based on thermodynamics. At a given temperature,equilibrium exists between water, hydrogen and oxygen according to thereaction H₂O→H₂+½O₂. The constant for this equilibrium, at a settemperature, can be expressed as K_(eq)=[(pH₂)*(pO₂)^(1/2)]/pH₂O. Basedon this equilibrium, it is evident that in the past the partial pressureof hydrogen, on the external surface of a platinum containing componentis determined by the partial pressure of water (e.g., the dew point)because the partial pressure of oxygen in air is fixed at 0.21atmospheres for air. Until the present invention, the only way toincrease the partial pressure of hydrogen at the external surface of theprecious metal, and thereby reduce the blister generation in the glassdue to hydrogen permeation, was to use a humidity control enclosure toincrease the dew point of the atmosphere around the system (see U.S.Pat. No. 5,785,726). However as described above, the present inventioneffectively reduces the partial pressure of oxygen at the externalsurface of the platinum containing component 115, 120, 122, 125, 127,130 and 132 which in turn increases the partial pressure of hydrogen atthe external surface of the platinum containing component 115, 120, 122,125, 127, 130 and 132 which reduces the blister generation in the glassdue to hydrogen permeation (see FIG. 5B). And, this can all be done bythe present invention without having to use a humidity control enclosureto change the dew point around the system 100 and 100′. As such with thepresent invention, even at the lowest dew point atmosphere of winter, itis possible to obtain a partial pressure of hydrogen on the externalsurface of the platinum containing component 115, 120, 122, 125, 127,130 and 132 that exceeds that of a 100° F. dew point day. FIGS. 5A and5B are schematics that illustrate the hydrogen permeation reactions thatoccur without and with the oxygen extraction technology of the presentinvention.

It should be appreciated that a majority of the hydrogen in the system100 and 100′ is generated because of the thermal breakdown of water atthe elevated temperatures encountered in the melting vessel 110. Thewater in the glass comes from chemically bound moisture in the glass andis proportional to the beta-OH of the glass. In addition, there is waterat the external surface of the system 100 and 100′ which comes frommoisture in the air and is proportional to the dew point of the air. Thewater at the external surface of the system 100 and 100′ also thermallybreaks down into hydrogen and oxygen at the elevated temperatures ofoperation.

It should also be appreciated that the partial pressure of hydrogen,under a given set of conditions, can be calculated based on the Gibbsfree energy for the reaction, H₂O→H₂+½O₂. For example, the free energy(G) for the water reaction is G=58,900−13.1 T. Where T is thetemperature in degrees Kelvin and G is the free energy in calories permole. At a given temperature, the equilibrium constant for the waterreaction can be calculated using the relationship K_(eq)=e^(−G/RT),where G and T are as previously noted and R is the gas constant. OnceK_(eq) is known, the ratio of the partial pressures of the various gasesinvolved in the water breakdown can be calculated whereK_(eq)=[(pH₂)*(pO₂)^(1/2])]/[pH₂O]. For example, at 1450° C., K_(eq) isequal to 2.47×10⁻⁵. If a 75° F. dew point air environment (pH₂O of 0.030atmospheres and pO₂ of 0.21 atmospheres) is heated to 1450° C., pH₂ iscalculated to be 1.59×10⁻⁶ atmospheres (1.59 ppm). And, if the partialpressure of hydrogen (1.59 ppm) is greater than the partial pressure ofhydrogen present at the glass/platinum interface then hydrogenpermeation blistering is suppressed.

Using the same equilibrium calculation, one can see that a decrease inthe partial pressure of oxygen will increase the partial pressure ofhydrogen, at a constant partial pressure of water (dew point). Thepresent invention takes advantage of this property and enables one tolower the partial pressure of oxygen at the glass/platinum interfacewhich causes the partial pressure of hydrogen on the exterior of thesystem 100 and 100′ to be greater than the partial pressure of hydrogenin the glass. As such, hydrogen now goes into the glass at a low levelwhich effectively suppresses the formation of oxygen blisters in theglass (see FIG. 5B).

In fact, calculations indicate that an atmosphere that has a dew pointof 10° F. can be made by the present invention to have a partialpressure of hydrogen higher than a 100° F. dew point air atmosphere.FIG. 6 shows a graph that illustrates this concept. In the graph, thepartial pressure of hydrogen is shown for a 10° F. and 40° F. dew pointatmosphere as a function of oxygen level. For reference, linesindicating the partial pressure of hydrogen for a 75° F. and 100° F. dewpoint air atmosphere are shown. This data indicates that the 10° F. dewpoint atmosphere will have a partial pressure of hydrogen greater thanthe 100° F. dew point air, if its partial pressure of oxygen is lessthan 0.01 percent.

Referring to FIG. 7, there is shown an experimental set-up 700 used toverify the oxygen extraction technology of the present invention. Theexperimental set-up 700 included a 0.435 inch diameter by 12 inch longtube of Pt—20Rh 702 that was closed on one end 702 a to be able to holdCorning Code 1737G glass 704. A three inch section of the tube 702, nearthe closed end 702 a, was plasma sprayed with a 0.010″ thick layer of Castabilized zirconia 706. On the external surface of the zirconia 706, aPt electrode 708 was made by painting a paste containing Pt powder in aring pattern around the circumference of the zirconia 706. Care wastaken to make sure that the Pt electrode 708 was electrically isolatedfrom the 0.435″ diameter Pt—20Rh tube 702. The purpose of the Ptelectrode 708 was to allow electrical contact to the external surface ofthe zirconia 706. Any other conductive material could have been used tomake this electrode 708. The tube 702 with the Pt electrode 708 on theexternal surface of the zirconia 706 was then fired at 1400° C. for 1hour to sinter the Pt together and drive off the organic binder. Afterfiring, the Pt electrode 708 made an electrically conductive surfaceover about 30% of the external surface of the zirconia 706. The glass704 was then placed inside the tube 702 to a level equivalent to theheight of the zirconia 706. A Pt lead wire 710 was wrapped around the Ptelectrode 708 on the external surface of the zirconia 706 to allow for apositive electrical connection to a DC power source 712. The bottom 6inches of the tube 702 was then suspended into a 1450° C. furnace 714.This caused the glass 704 inside the tube 702 to melt. A ⅛″ diameter Ptrod 716 was inserted inside the Pt tube 702 to the point where the tipof the rod 716 was immersed in the molten glass 704 about ½ inch. Theportion of this rod 716 above the glass 704 was sheathed with an aluminasleeve 718 to prevent the rod 716 from electrically contacting theinside surface of the Pt tube 702. A Pt lead wire 720 was connected tothe Pt tube 702 to allow for a negative electrical connection to the DCpower source 712. The DC potential between the rod 716 and tube 702 wasmonitored using a voltage monitor 722. The measured DC potential wasindicative of the partial pressure of oxygen at the two Pt/glassinterfaces. It was assumed that the partial pressure of oxygen at theinterface of the Pt rod 716 and glass 704 is close to being equilibratedwith air. And, an estimate of the partial pressure of oxygen at theinterface of the Pt tube 702 and glass 704 can be made using the Nernstequation. This data, with the conversion of potential to partialpressure of oxygen is provided in the graph shown in FIG. 8.

Referring to the graph shown in FIG. 8, it is apparent that extractingoxygen from the external surface of the Pt tube 702 has an effect on theoxygen level at the internal interface of the Pt tube 702 and glass 704.As soon as the current is applied across the coating of zirconia 706 toremove oxygen, a shift was seen in the partial pressure of oxygen on theinternal surface of the Pt tube 702. There is a gradual continueddownward trend in the partial pressure of oxygen on the internal surfaceof the Pt tube 702 due to the kinetics of oxygen removal from thisinterface. This reaction is reversed when the current is turned off. Theinternal surface of the Pt tube 702 begins to re-oxidize. This behavioris typical to what is seen when the dew point on the external surface ofthe Pt tube 702 is changed. Historic data for this is provided in thegraph shown in FIG. 9.

Referring to the graph shown in FIG. 9, it is apparent that the dewpoint surrounding the Pt tube 702 was decreased in several steps. Adecrease in dew point lowered the partial pressure of hydrogen on theoutside of the Pt tube 702, leading to an increase in hydrogenpermeation. This was seen as an increase in the partial pressure ofoxygen at the internal interface of the Pt tube 702 and glass 704. Thus,the experimental results shown in FIGS. 8 and 9 show similar behaviors,a higher partial pressure of hydrogen at the external surface of the Pttube 702 results in a lowering of the oxygen level at the interface ofthe Pt tube 702 and glass 704, because it was stopping hydrogenpermeation. Whereas, a decrease in the partial pressure of hydrogen atthe external surface of the Pt tube 702 results in an increase in theoxygen level at the interface of the Pt tube 702 and glass 704, becauseof the increase in hydrogen permeation. Moreover, the data clearly showsthat the application of 2 amps of current to a 4 in² area of Pt causedmore of a shift in the partial pressure of oxygen than a 60° F. shift indew point. This indicates that the zirconia oxygen extraction system ofthe present invention is capable of a broader range of protection thanthe traditional humidity control enclosure disclosed in U.S. Pat. No.5,758,726.

Following are some advantages and uses of the system 100 and 100′ andmethod 200 of the present invention:

-   -   The present invention also reduces the oxidation of the external        surfaces of the platinum containing components. Current        technology relies on a coating, such as Rokide (aluminum oxide)        on the outer surface of platinum containing components to limit        the contact of air (oxygen) with the precious metal. This        invention provides a means of lowering the oxygen level, which        is a key driver in the oxidation reaction of platinum.    -   The present invention provides a means of controlling the        partial pressure of oxygen around the external surface of the        system, without the use of an enclosure or secondary vessel to        control the atmosphere around the system.    -   The present invention is particularly useful for forming high        melting or high strain point glass sheets like the ones used in        flat panel displays.    -   The present invention provides an alternative to changing the        batch constituents of the glass, such as, for example, the        addition of arsenic-containing materials to the glass batch. In        addition, the present invention provides an alternative to using        low water containing batch constituents to make the glass.    -   The present invention could help anyone who melts, delivers or        forms glass in a platinum-containing vessel. In addition, the        present invention could be beneficial in the manufacturing of        Vycor tubing and sheet. Moreover, the present invention could be        beneficial in the manufacturing on non-LCD glass.    -   The present invention can be used in any glass or melting system        in which glass comes in contact with refractory metals such as        Pt, Mo, Rh and alloys. This contact could be in the melting,        delivery or forming phase of production.    -   If there is a process instability or change in the water content        of the glass that leads to an increase in hydrogen permeation        blistering, then there is often no way to respond to this        problem using the traditional humidity control enclosure since        it may be operating at its maximum dewpoint. The present        invention has a better chance of solving this problem.    -   Preferred oxygen ion transportable materials that can be used in        the present invention are yttria stabilized zirconia or Ca        stabilized zirconia. Other types of oxygen ion transportable        materials can be used as well such as partially stabilized        zirconias doped with yttria and Ca, and partially and fully        stabilized zirconias doped with oxides of Sc, Nd, Sm, Eu, Gd,        Tb, Dy, Ho, Er, Tm, Yb, Lu and Mg. CeO2, TiO2, SnO2, YNbO4,        YTaO4, rare earth niobates/tantalates also can stabilize or        partially stabilize the cubic and or tetragonal phases, but        create fewer oxygen vacancies in the zirconia lattice reducing        the ionic conductivity and are not as preferred. Mixtures of the        above listed dopants can be used. Zirconias normally have hafnia        levels of 1-10%. Hafnia and mixtures of hafnia and zirconia with        dopants can be used, but cost more. Numerous other oxygen ion        conductors such as doped lanthanum gallate have been discovered        and can be used when their melting points, oxygen partial        pressure stability regions, and low electronic conductivity        regions are not exceeded. It should be appreciated that there        are many ways to apply the oxygen ion transportable materials,        one such way is to use plasma spraying. The coating of oxygen        ion transportable materials need not be fully dense but should        be somewhat impervious to oxygen gas (O₂).    -   It should also be appreciated that it is also possible to        prevent hydrogen permeation and the subsequent blister        generation by a method/system that allows a reduced oxygen        atmosphere to be maintained or created around the external        non-glass contact surface of the system 100 and 100′ or even a        traditional system. A potential means of achieving the reduced        partial pressure of oxygen would be to enclose the external        surface or a part of the surface of the system 100 and 100′ in a        container that has a low oxygen content gas flowing into it.        This would form an atmosphere such that the formation of        hydrogen gas from the breakdown of moisture in the atmosphere is        favored. This could be used to improve a traditional system and        could also be used in conjunction with the present invention to        obtain a higher partial pressure of hydrogen even at very low        dewpoint conditions.    -   The refractory metal component used in the vessels of the system        100 and 100′ can include a metal selected from the group of        platinum, molybdenum, palladium, rhodium and alloys thereof.

Although two embodiments of the present invention have been illustratedin the accompanying Drawings and described in the foregoing DetailedDescription, it should be understood that the invention is not limitedto the embodiments disclosed, but is capable of numerous rearrangements,modifications and substitutions without departing from the spirit of theinvention as set forth and defined by the following claims.

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 17. A glass material formed by a manufacturing processperformed within a system that includes: a melting, fining, delivery,mixing or forming vessel, the vessel includes a refractory metalcomponent having an inner wall that contacts the glass and an outer wallcoated with an oxygen ion transportable material which is then coatedwith a conductive electrode; and a DC power source having a negativepower lead connected to the refractory metal component and a positivepower lead connected to the conductive electrode.
 18. The glass materialof claim 17, wherein when said DC power source supplies DC power acrossthe oxygen ion transportable material then oxygen ions migrate from therefractory metal component to the conductive electrode and enables oneto control the partial pressure of oxygen around an exterior of thevessel which helps one to effectively suppress the formation ofundesirable gaseous inclusions and surface blisters within said glassmaterial.
 19. The glass material of claim 18, wherein said DC powersource in addition to enabling one to control the partial pressure ofoxygen around the exterior of the vessel also helps one to effectivelyreduce the oxidation of external, non-glass contact surfaces of therefractory metal component.
 20. The glass material of claim 17, whereinsaid DC power source is capable of supplying adjustable DC power whichenables one to control the rate of the oxygen migration from therefractory metal component to the conductive electrode which enables oneto control a magnitude of the partial pressure of oxygen to be within arange of about 1 to 10⁻¹⁰ atmospheres around the exterior of the vessel.21. The glass material of claim 17, wherein said refractory metalcomponent includes a metal selected from the group of platinum,molybdenum, palladium, rhodium and alloys thereof.
 22. The glassmaterial of claim 17, wherein said oxygen ion transportable materialincludes partially or fully stabilized zirconia.
 23. The glass materialof claim 17, wherein said manufacturing process is a fusionmanufacturing process.
 24. The glass material of claim 17, wherein saidglass material is a glass sheet.
 25. The glass material of claim 17,wherein said glass material is a glass tube.